Progesterone as an autocrine/paracrine regulator of human granulosa cell proliferation

Progesterone Signaling and Mammalian Ovarian Follicle Growth Mediated by Progesterone Receptor Membrane Component Family Members

How progesterone influences ovarian follicle growth is a difficult question to answer because ovarian cells synthesize progesterone and express not only the classic nuclear progesterone receptor but also members of the progestin and adipoQ receptor family and the progesterone receptor membrane component (PGRMC) family. Which type of progestin receptor is expressed depends on the ovarian cell type as well as the stage of the estrous/menstrual cycle. Given the complex nature of the mammalian ovary, this review will focus on progesterone signaling that is transduced by PGRMC1 and PGRMC2 specifically as it relates to ovarian follicle growth. PGRMC1 was identified as a progesterone binding protein cloned from porcine liver in 1996 and detected in the mammalian ovary in 2005. Subsequent studies focused on PGRMC family members as regulators of granulosa cell proliferation and survival, two physiological processes required for follicle development. This review will present evidence that demonstrates a causal relationship between PGRMC family members and the promotion of ovarian follicle growth. The mechanisms through which PGRMC-dependent signaling regulates granulosa cell proliferation and viability will also be discussed in order to provide a more complete understanding of our current concept of how progesterone regulates ovarian follicle growth.

Progesterone receptor membrane component 1 and 2 regulate granulosa cell mitosis and survival through a NFΚB-dependent mechanism†

Progesterone receptor membrane component 1 (PGRMC1) interacts with PGRMC2, and disrupting this interaction in spontaneously immortalized granulosa cells (SIGCS) leads to an inappropriate entry into the cell cycle, mitotic arrest, and ultimately cell death. The present study revealed that PGRMC1 and PGRMC2 localize to the cytoplasm of murine granulosa cells of nonatretric follicles with their staining intensity being somewhat diminished in granulosa cells of atretic follicles. Compared to controls (Pgrmc1fl/fl), the rate at which granulosa cells entered the cell cycle increased in nonatretic and atretic follicles of mice in which Pgrmc1 was conditionally deleted (Pgrmc1d/d) from granulosa cells. This increased rate of entry into the cell cycle was associated with a ≥ 2-fold increase in follicular atresia and the nuclear localization of nuclear factor-kappa-B transcription factor P65; (NFΚB/p65, or RELA). GTPase activating protein binding protein 2 (G3BP2) binds NFΚB/p65 through an interaction with NFΚB inhibitor alpha (IκBα), thereby maintaining NFΚB/p65's cytoplasmic localization and restricting its transcriptional activity. Since PGRMC1 and PGRMC2 bind G3BP2, studies were designed to assess the functional relationship between PGRMC1, PGRMC2, and NFΚB/p65 in SIGCs. In these studies, disrupting the interaction between PGRMC1 and PGRMC2 increased the nuclear localization of NFΚB/p65, and depleting PGRMC1, PGRMC2, or G3BP2 increased NFΚB transcriptional activity and the progression into the cell cycle. Taken together, these studies suggest that PGRMC1 and 2 regulate granulosa cell cycle entry in follicles by precisely controlling the localization and thereby the transcriptional activity of NFΚB/p65.

Progesterone Actions During Central Nervous System Development

Although progesterone is a steroid hormone mainly associated with female reproductive functions, such as uterine receptivity and maintenance of pregnancy, accumulating data have shown its physiological actions to extend to several non-reproductive functions in the central nervous system (CNS) both in males and females. In fact, progesterone is de novo synthesized in specific brain regions by neurons and glial cells and is involved in the regulation of various molecular and cellular processes underlying myelination, neuroprotection, neuromodulation, learning and memory, and mood. Furthermore, progesterone has been reported to be implicated in critical developmental events, such as cell differentiation and neural circuits formation. This view is supported by the increase in progesterone synthesis observed during pregnancy in both the placenta and the fetal brain. In the present review, we will focus on progesterone actions during CNS development.

A Higher Estradiol Rise After Dual Trigger in Progestin-Primed Ovarian Stimulation Is Associated With a Lower Oocyte and Mature Oocyte Yield in Normal Responders

Background: Prior studies have shown that patients with a >10% estradiol (E₂) rise after trigger had more oocytes retrieved than plateauing or decreasing E₂ responders. However, multiple follicles develop at different stages of maturation during controlled ovarian stimulation (COS) and may exhibit different responses to trigger. The association between the magnitude of E₂ increase and oocyte retrieval outcomes is still unclear. Methods: This was a retrospective cohort study of 2,898 women undergoing their first COS cycles with normal response from January 2014 to December 2017 at a tertiary-care academic medical center. Patients were categorized into five groups according to the percentage increase in E₂ levels before and after dual trigger: <10.0%, 10.0-19.9%, 20.0-29.9%, 30.0-39.9%, and ≥40.0%. Univariable and multivariable linear regression analysis were performed to explore the association between E₂ increase and oocyte/mature oocyte yield, while logistic regression was used to assess its effect on low oocyte/mature oocyte yield (<10th percentile). Results: The post-trigger E₂ increase was negatively associated with both oocyte yield (P-trend < 0.001, adjusted P-trend = 0.033) and mature oocyte yield (P-trend < 0.001, adjusted P-trend = 0.002). Compared with a <10.0% E₂ increase after trigger, patients with a ≥40.0% rise had fewer mature oocyte yield [adjusted mean absolute difference [MD] = -5.2, 95% confidence interval [CI]: -8.2--1.8] and higher risk of low mature oocyte yield (adjusted odds ratio [OR] = 1.64, 95% CI: 1.04-2.60), whereas no statistical significance was found in oocyte yield (adjusted MD = -2.7, 95% CI: -6.1-0.8) and low oocyte yield (adjusted OR = 1.48, 95% CI: 0.96-2.28). In addition, the rates of implantation, positive pregnancy test, clinical pregnancy, ongoing pregnancy, pregnancy loss, and live birth were comparable among the 1,942 frozen embryo transfer cycles with embryos originating from different groups of E₂ increase (all P > 0.05). Conclusions: A higher E₂ rise after dual trigger is independently associated with a lower oocyte and mature oocyte yield in normal responders. Further studies are needed to explore the efficacy of individualized time interval from trigger to oocyte retrieval based on the magnitude of E₂ increase after trigger.

In vitro progesterone production by luteinized human mural granulosa cells is modulated by activation of AMPK and cause of infertility

BACKGROUND

Mural granulosa cells from IVF patients were provided by the West Virginia University Center for Reproductive Medicine in Morgantown, WV. The effect of adenosine monophosphate activated protein kinase (AMPK) activation, primary cause of infertility, age, BMI, and pregnancy outcome on production of progesterone were examined separately.

METHODS

Isolated mural sheets from IVF patients (n = 26) were centrifuged, supernatant discarded, and the pellet re-suspended in 500 μl of DMEM/F12. Mural granulosa cells were plated at 10,000 cells/well in triplicate per treatment group with 300 μl DMEM/F12 media at 37 °C and 5% CO2 in a humidified incubator to permit luteinization. Four days after initial plating, cells were treated with either an AMPK inhibitor, DM; an AMPK activator, AICAR; or hCG. Cells were cultured for 24 h after treatment when medium was collected and frozen at -20 °C until assayed for P4 by radioimmunoassay.

RESULTS

The AMPK activator, AICAR, inhibited P4 production (P < 0.001), whereas the AMPK inhibitor, DM, did not affect basal P4 (P < 0.05). Progesterone production increased when cells from patients whose primary cause of infertility was a partner having male infertility were treated with hCG compared to control (P = 0.0045), but not in patients with other primary infertility factors (P > 0.05). Additionally, hCG increased P4 production in patients between the ages 30-35 (P = 0.008) and 36-39 (P = 0.04), but not in patients ages 25-29 (P = 0.73). Patients with normal BMI had increased P4 production when treated with hCG (P < 0.0001), however there was no change in P4 production from cells of patients who were overweight or obese (P > 0.05). Cells from patients who became pregnant to IVF had greater P4 production when stimulated with hCG than those who did not become pregnant when compared to controls (P > 0.05).

CONCLUSIONS

Understanding how AMPK activation is regulated in ovarian cells could lead to alternative or novel infertility treatments. Human mural granulosa cells can serve as a valuable model for understanding how AMPK affects P4 production in steroidogenic cells. Additionally, when stimulated with hCG, P4 production by mural granulosa cells differed among infertility type, age, BMI, and pregnancy outcome.

Expression of progesterone receptor membrane component-2 within the immature rat ovary and its role in regulating mitosis and apoptosis of spontaneously immortalized granulosa cells

Progesterone receptor membrane component 2 (Pgrmc2) mRNA was detected in the immature rat ovary. By 48 h after eCG, Pgrmc2 mRNA levels decreased by 40% and were maintained at 48 h post-hCG. Immunohistochemical studies detected PGRMC2 in oocytes and ovarian surface epithelial, interstitial, thecal, granulosa, and luteal cells. PGRMC2 was also present in spontaneously immortalized granulosa cells, localizing to the cytoplasm of interphase cells and apparently to the mitotic spindle of cells in metaphase. Interestingly, PGRMC2 levels appeared to decrease during the G1 stage of the cell cycle. Moreover, overexpression of PGRMC2 suppressed entry into the cell cycle, possibly by binding the p58 form of cyclin dependent kinase 11b. Conversely, Pgrmc2 small interfering RNA (siRNA) treatment increased the percentage of cells in G1 and M stage but did not increase the number of cells, which was likely due to an increase in apoptosis. Depleting PGRMC2 did not inhibit cellular (3)H-progesterone binding, but attenuated the ability of progesterone to suppress mitosis and apoptosis. Taken together these studies suggest that PGRMC2 affects granulosa cell mitosis by acting at two specific stages of the cell cycle. First, PGRMC2 regulates the progression from the G0 into the G1 stage of the cell cycle. Second, PGRMC2 appears to localize to the mitotic spindle, where it likely promotes the final stages of mitosis. Finally, siRNA knockdown studies indicate that PGRMC2 is required for progesterone to slow the rate of granulosa cell mitosis and apoptosis. These findings support a role for PGRMC2 in ovarian follicle development.

Non-canonical progesterone signaling in granulosa cell function

It has been known for over 3 decades that progesterone (P4) suppresses follicle growth. It has been assumed that P4 acts directly on granulosa cells of developing follicles to slow their development, as P4 inhibits both mitosis and apoptosis of cultured granulosa cells. However, granulosa cells of developing follicles of mice, rats, monkeys, and humans do not express the A or B isoform of the classic nuclear receptor for P4 (PGR). By contrast, these granulosa cells express other P4 binding proteins, one of which is referred to as PGR membrane component 1 (PGRMC1). PGRMC1 specifically binds P4 with high affinity and mediates P4's anti-mitotic and anti-apoptotic action as evidenced by the lack of these P4-dependent effects in PGRMC1-depleted cells. In addition, mice in which PGRMC1 is conditionally depleted in granulosa cells show diminished follicle development. While the mechanism through which P4 activation of PGRMC1 affects granulosa cell function is not well defined, it appears that PGRMC1 controls granulosa cell function in part by regulating gene expression in T-cell-specific transcription factor/lymphoid enhancer factor-dependent manner. Clinically, altered PGRMC1 expression has been correlated with premature ovarian failure/insufficiency, polycystic ovarian syndrome, and infertility. These collective studies provide strong evidence that PGRMC1 functions as a receptor for P4 in granulosa cells and that altered expression results in compromised reproductive capacity. Ongoing studies seek to define the components of the signal transduction cascade through which P4 activation of PGRMC1 results in the regulation of granulosa cell function.

Plasminogen activator inhibitor 1 RNA-binding protein interacts with progesterone receptor membrane component 1 to regulate progesterone's ability to maintain the viability of spontaneously immortalized granulosa cells and rat granulosa cells

Progesterone receptor membrane component 1 (PGRMC1) mediates the antiapoptotic action of progesterone (P4). PGRMC1 interacts with plasminogen activator inhibitor 1 RNA-binding protein (PAIRBP1), but the functional significance of this interaction is unknown. To examine the function of PGRMC1-PAIRBP1 interaction, PAIRBP1 was depleted from spontaneously immortalized granulosa cells (SIGCs) and the effects on the expression and localization of PGRMC1 as well as P4's ability to bind to SIGCs and prevent apoptosis was assessed. Depleting PAIRBP1 enhanced cellular (3)H-P4 binding and did not alter the expression or cellular localization of PGRMC1 but attenuated P4's antiapoptotic action. Transfection of a PGRMC1-green fluorescent protein (GFP) peptide mimic, which binds PAIRBP1 as demonstrated by in situ proximity assay, doubled the rate at which SIGCs undergo apoptosis compared to cells transfected with either the empty GFP expression vector or Pairbp1 small interfering RNA. Moreover, P4 did not prevent these cells from undergoing apoptosis. Similar studies conducted with granulosa cells isolated from immature rats also showed that PGRMC1 interacts with PAIRBP1 and that transfection of PGRMC1-GFP peptide mimic accelerates the rate of granulosa cell apoptosis by 4-fold even in the presence of serum and P4. These studies support the concept that the interaction between PAIRBP1-PGRMC1 is an essential component of the mechanism through which P4 inhibits apoptosis. Surprisingly, PGRMC1-PAIRBP1 interaction is not required for P4 binding or the cellular localization of PGRMC1 but rather appears to couple PGRMC1 to downstream components of the P4-PGRMC1 signal transduction pathway.

Ovarian FAM110C (family with sequence similarity 110C): induction during the periovulatory period and regulation of granulosa cell cycle kinetics in rats

FAM110C belongs to a family of proteins that regulates cell proliferation. In the present study, the spatiotemporal expression pattern of FAM110C and its potential role were examined during the periovulatory period. Immature female rats were injected with equine chorionic gonadotropin (eCG) followed by human chorionic gonadotropin (hCG) and ovaries or granulosa cells were collected at various times after hCG administration (n = 3/time point). Expression levels of Fam110c mRNA and protein were highly induced both in intact ovaries and granulosa cells at 8 to 12 h after hCG treatment. In situ hybridization analysis demonstrated Fam110c mRNA expression was induced in theca and granulosa cells at 4 h after hCG, primarily localized to granulosa cells at 8 h and 12 h, and decreased at 24 h after hCG. There was negligible Fam110c mRNA detected in newly forming corpora lutea. In rat granulosa cell cultures, hCG induced expression of Fam110c mRNA was inhibited by RU486, whereas NS398 and AG1478 had no effect, suggesting that Fam110c expression is regulated in part by the progesterone receptor pathway. Promoter activity analysis revealed that an Sp1 site was important for the induction of Fam110c expression by hCG. Overexpression of FAM110C promoted granulosa cells to arrest at the G(1) phase of the cell cycle but did not change progesterone levels. In summary, hCG induces Fam110c mRNA expression in granulosa cells by activation of an Sp1-binding site and the actions of progesterone. Our findings suggest that FAM110C may control granulosa cell differentiation into luteal cells by arresting cell cycle progression.

Expression of the insulin-like growth factor and insulin systems in the luteinizing macaque ovarian follicle

OBJECTIVE

To determine intrafollicular hormone levels and characterize the mRNA expression of the insulin-like growth factor (IGF) receptors, IGF binding proteins (IGFBP), and pregnancy-associated plasma protein-A (PAPP-A) in granulosa cells before and after an ovulatory hCG stimulus.

DESIGN

Experimental animal study.

SETTING

Academic medical center.

ANIMAL(S)

Adult rhesus macaques.

INTERVENTION(S)

Animals received exogenous FSH to promote the development of multiple preovulatory follicles. Follicles were aspirated before (0 hours) or 3, 6, 12, or 24 hours after an ovulatory hCG bolus.

MAIN OUTCOME MEASURE(S)

IGF1, IGF2, and insulin levels in follicular fluid were determined by radioimmunoassay. Messenger RNA (mRNA) levels in granulosa cells were determined by real-time reverse transcriptase-polymerase chain reaction. IGFBPs and PAPP-A in follicular fluid were determined by Western blot analysis and enzyme-linked immunosorbent assay.

RESULT(S)

IGF1, IGF2, and insulin in follicular fluid did not change during luteinization. IGF1R, IGFBP1, and IGFBP2 mRNAs were unchanged by hCG. IGF2R, IGFBP3, -5, and -6 and PAPP-A mRNA levels increased after hCG administration, while insulin receptor and IGFBP4 mRNA levels decreased after hCG administration. IGFBP3 and -6 and PAPP-A protein increased after hCG administration.

CONCLUSION(S)

Dynamic changes in the expression of the IGFBPs and PAPP-A suggest tight regulation of IGF action during ovulation and corpus luteum formation.

Increased progesterone secretion and 3 beta-hydroxysteroid dehydrogenase activity in human cumulus cells by pregnenolone is limited to the high steroidogenic active cumuli

PURPOSE

Several reports imply that lower progesterone secretion by cumulus-oocyte complexes (COCs) is associated with lower fertilization in the corresponding oocyte. The possible role of progesterone in oocyte fertilization in humans was studied using two approaches: (a) increasing the total progesterone secretion by culturing more than one COC per dish; and (b) increasing the cumulus cell progesterone secretion by providing pregnenolone as a substrate.

METHODS

Mature COCs were cultured individually or cocultured in groups. Oocyte fertilization and progesterone secretion were tested after 20 hr and 3 days in culture, respectively. The cumuli from individually plated COCs were cultured in the absence of oocyte for an additional 3 days in order to test the effects of pregnenolone on progesterone secretion and the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity. A comparable study with pregnenolone was performed on the corresponding granulosa-lutein cells.

RESULTS

Increasing the number of COC to two instead of one led to a significant increase in both fertilization rate and progesterone secretion. The addition of pregnenolone during days 3-6 increased significantly both progesterone secretion and 3 beta-HSD activity. Comparable results were observed in granulosa-lutein cells subjected to pregnenolone treatment. Following the first 3 days culture, cumulus masses were categorized as secreting high or low progesterone levels. Adding pregnenolone had a greater effect on both progesterone secretion and 3 beta-HSD activity in the high-progesterone-secreting cumuli.

CONCLUSIONS

Addition of pregnenolone increased progesterone secretion and 3 beta-HSD more efficiently in the higher-progesterone-secreting cumuli. Coculture of two COCs instead of one led to a higher fertilization rate and greater progesterone secretion.

Regulation of ovarian follicle differentiation in gonadotrophin-stimulated rats

The aim of the present study was to investigate the regulation of the in vitro DNA synthesis of ovarian cells recovered from prepubertal rats 48 h after administration of pregnant mare's serum gonadotrophin alone (granulosa cells) or followed by human chorionic gonadotrophin (luteal cells). Isolated granulosa cells were cultured in serum-free medium, different stimuli added for periods of 48 h, and 3H-thymidine incorporation was measured. Both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) inhibited 3H-thymidine incorporation by cultured granulosa cells in a dose-dependent manner (FSH: 10, 100, 200 ng/mL = 26, 41, 49% inhibition, respectively; LH: 0.1, 1, 10 ng/mL = 11, 37, 75% inhibition, respectively). On the other hand, estradiol was found to stimulate 3H-thymidine incorporation in granulosa cells (Estradiol: 5, 50, 500 ng/mL = 17, 37, 76% stimulation, respectively). In luteal cells, the rate of basal 3H-thymidine incorporation was very low (granulosa cells: 2560 +/- 310; luteal cells: 661 +/- 92 cpm/100,000 cells) and not modified by any stimulus. To determine the possible production of an inhibitory growth factor by the early corpus luteum, 3H-thymidine incorporation by granulosa cells was assessed in the presence of 10% conditioned media (CM) recovered from luteal cell cultures. A marked inhibition both in basal and estradiol-stimulated 3H-thymidine incorporation was observed (74 and 76% of inhibition, respectively). Results suggest that an inhibitory growth factor produced by luteal cells after luteinizing gonadotrophin stimulus could be involved in the differentiation of growing follicles to corpus luteum.